SPR L7 Perception and Attention

Question 1

Perception

Learning Outcomes (for general perusal)

Answer 1

• What is perception?
• What is signal detection?
• How do we determine quantitative differences between stimuli?
• Organising the perceptual world: Gestalt Theory
• Depth & Distance Perception
• Integrating percepts from different senses
• When things go wrong

Question 2

What is Perception?

1. what is Sensation?
2. what is perception?
   
   1. ​What does it combine?
   2. What does it influence?

Answer 2

1. The action of a stimulus upon receptors of a sense organ and the resulting electrical signals sent to the brain for processing
2. The mind’s interpretation of sensations – i.e. how we make sense of what we see, hear, taste, touch, and smell:
   
   1. Combines knowledge and understanding of the world, so that sensations become meaningful experiences (Personal experience of the world)
   2. our thoughts, feelings, actions.

Question 3

Stimulus Detection

1. What does our perceptual system ask at it most basic level?
2. What does Psychophysics focus on?

Answer 3

1. Is there anything out there? (i.e. can we detect a stimulus in the environment?) Has a change occurred in a stimulus? Are two stimuli quantitatively different?
2. the relationship between the physical energy of a stimulus (Sensation) and the psychological experience of that stimulus (Perception).

Question 4

Absolute Thresholds

1. What does ‘absolute threshold’ mean?
2. Give some examples of human sense and absolute thresholds

Answer 4

1. The minimum detectable amount of a physical energy
2. See picture

• Hearing - watch tick under quiet conditions at 20ft
• Taste - 1tsp of sugar in 2 gallons of water

Question 5

Absolute Threshold

Sometimes the same stimulus will be detected, other times not

Why?

(outine internal noise and response criterion)

Therefore, give a definiton of AT and show it on the graph

Answer 5

• Internal noise: ‘snow’ - the spontaneous random firing of neurons
• Response criterion: willingness/reluctance to respond, expectation etc. Reflects a person’s motivation and current/past experience.

defined as the intensity at which the signal is detected with 50% of the time.

Question 6

Judging Quantitative Differences between Stimuli

1. What happens to the ability to detect physical differences in a stimulus as the magnitude of the stimulus increases?
2. What does the Weber-Fechner Law state?
   
   1. Describe the constant fraction (K) for different types of sensory inputs

Answer 6

1. it declines
2. the smallest detectable (i.e. perceived) difference in stimulus energy (called the difference threshold or just-noticable difference [JND]) is a constant fraction of the intensity or amount of the stimulus (I).
   1. The constant fraction [K] is different for different types of sensory inputs (sensitivity determined by evolutionary importance of sense to organism).

Question 7

State Weber’s Law

What does this law not work for?

Answer 7

Weber’s Law: JND=KI

the smallest detectable (i.e. perceived) difference in stimulus energy (JND) is a constant fraction of the intensity or amount of the stimulus (I).

Does not work for very weak/very intense stimuli, but does cover both simple and complex stimuli.

Question 8

Weber’s Law

Weber’s Constants are attached

1. What is the JND when holding a 1kg object?
2. What is the JND when holding a 2kg object?

Answer 8

1. JND = 0.02 x 1kg = 20g
2. JND = 0.02 x 2kg = 40g

Question 9

Perceptual Organisation:
Gestalt Theory

1. What does ‘Gestalt’ roughly mean?
2. What does this theory propose?
3. List the series of laws/princples that these are expressed as

Answer 9

1. ‘whole figure/
2. The whole figure is greater than the sum of its parts. The inherent properties of a stimulus leads us to group (or glue) them together.
3. Proximity, Similarity, Closure, Continuity, Law of Pragnanz: Simplicity

Question 10

Perceptual Organisation:
Gestalt Theory

Outline how the whole figure is seen as greater than the sum of its parts.

Answer 10

Shapes put together become completely different, added dimensions etc.

Question 11

Perceptual Organistaion: Gestalt Theory

Describe the Law of Proximity

Answer 11

things that are near each other seem to be grouped together

Question 12

Perceptual Organistaion: Gestalt Theory

Describe the Law of Similarity

Answer 12

things which are similar in some way appear to be grouped together.

Question 13

Perceptual Organistaion: Gestalt Theory

Describe the Law of Closure

Answer 13

Objects grouped together are seen as a whole.

We tend to ignore gaps and complete contour lines.

(In the image there are no triangles or circles, but our minds fill the missing information to create familiar shapes and images)

Question 14

Perceptual Organistaion: Gestalt Theory

Describe the Law of Continuity

Answer 14

Lines are seen as following the smoothest path

(see image)

Question 15

Perceptual Organistaion: Gestalt Theory

Describe the Law of Pragnanz (Simplicity)

Answer 15

Reality is organised or reduced to the simplest form possible

Question 16

Depth & Distance Perception

How do we perceive depth (3D) & distance from a 2D retinal image?

1. Where are images percieved?
2. What is the Distal Stimulus?
3. What is the Proximal Stimulus?
4. What is the Percept?
5. What are the contributors to depth perception?

Answer 16

1. in the cerebral cortex, not on the retina of the eye
2. 3D Physical Object
3. Proximal Stimulus: 2D ‘Image’ on Retinal Surface
4. Mental Representation (i.e. Perception)
5. 1. Stimulus cues (monocular cues: only one eye needed)
6. Cues based on properties of visual system (binocular cues)

Question 17

Depth Perception:
Static Stimulus Cues

Describe Light and shadow: where do we assume assume illumination comes from?

Answer 17

above

Question 18

Depth Perception:
Static Stimulus Cues

What are these?

Answer 18

• Relative size
• Interposition or occlusion
• Reduced clarity
• Textural gradient
• Linear perspective

Question 19

Depth Perception: Illusions

Why do illusions occur?

Answer 19

Illusions occur, in part, because the perceptual system is so active, constantly filling in gaps and providing interpretations that go beyond information provided by the senses.

Question 20

Depth Cues from the Visual System

What are the following?

1. Accommodation
2. Convergence
3. Binocular Disparity
4. Proprioception

Answer 20

1. lens changes shape to bring an image into focus on the retina. Muscles surrounding lens must tighten or relax. Proprioceptive information is relayed to the brain.
2. muscles of the eye must rotate inward to project image onto retina. Proprioceptive information is relayed to the brain.
3. differences between the two retinal images as a result of their different spatial locations. Disparity reduces with increasing distances.
4. the sense that indicates whether the body is moving with required effort, as well as where the various parts of the body are located in relation to each other. Stimuli from within the body.

Question 21

Perception:
When things go wrong

Describe the following

1. Blindsight
2. Spaitial Neglect
3. Agnosia

Answer 21

1. people cannot consciously see a certain portion of their visual field but still behave in some instances as if they can see it.
2. after damage to one hemisphere of the brain, a deficit in attention to the opposite side of space is observed.
3. loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss.

Question 22

What is Blindsight?

Answer 22

people cannot consciously see a certain portion of their visual field but still behave in some instances as if they can see it.

http://tinyurl.com/cu95eqf

Question 23

Unilateral Spatial Neglect

1. What is spatial neglect?
2. What is it most frequently associated with?

Answer 23

1. after damage to one hemisphere of the brain, a deficit in attention to the opposite side of space is observed.
2. lesions to right parietal lobe (yellow)

Contralateral spatial deficit = deficit observed on left side

Question 24

Agnosia

1. What is agnosia?
2. What is it associated with?

Agnosia patient (HJA) describes a carrot:

• “A carrot is a root vegetable cultivated and eaten as human consumption worldwide”.
• A carrot is then presented visually: “I have not the glimmerings of an idea what that is. The bottom points seem solid, and the other bits are feathery. It does not seem to be logical unless it is some sort of brush”.

Answer 24

1. loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss.
2. occipital/temporal cortex damage.

Question 25

A Special Type of Agnosia:
Prosopagnosia

1. What is prosopagnosia?
2. Where are the lesions?
3. What is Capgras Syndrome? http://tinyurl.com/nmn5cv

Answer 25

1. (sometimes known as face blindness) is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact. See picture.
2. Fusiform Gyrus
3. Recognise faces, but believe they are imposters:

Sensation + Emotion = Perception?

Question 26

Reading:
Perception

1. What are the 5 primary features of perception
2. Describe bottom-up and top-down processing.
3. What factors affect our ability to control our perceptions?
4. What factors influence our perceptions in a social context?

Question 27

Auditory Perception (5 minutes)

Answer 27

Go to youtube and find the “virtual barber shop”

www.youtube.com/watch?v=IUDTlvagjJA

You will need a set of headphones for this experience to work.

Think about the distance cues (perceived loudness) and spatial cues provided: disparity between the ears equivalent to binocular disparity.

Can auditory information trigger the experience of other perceptual experiences (e.g. tactile – did you feel a sensation that your hair was actually being cut?). Sensations can cause incorrect percepts!